Container-dwelling mosquitoes are medically important, with Aedes albopictus, Ochlerotatus triseriatus, Culex pipiens/quinquefasciatus, among others, acting as vectors of human diseases. Arrivals in North America of successive invasive container mosquitoes, including, among others Aedes albopictus, and more recently Ochlerotatus japonicus, are important because these species can act as vectors, but also because they alter the organization of the community and in so doing may have indirect impacts on human disease. Understanding the ecology of container communities and their invaders will be a valuable tool for understanding how, where, and when mosquitoes in these human-associated habitats may become health threats. To understand how multispecies assemblages of interacting mosquitoes may affect one another directly and indirectly, and the consequences of those effects for vector populations, this project has 3 specific aims. Specific aim 1 is to determine the roles of direct and indirect effects among competing species of Aedes and Ochlerotatus. We will use a statistical design for detecting indirect effects in a laboratory experiment involving 4 species to test the hypothesis that indirect effects of competing species affect mosquito population dynamics. In a related field experiment, we will use a similar design to test the hypothesis that in nature, direct and indirect effects of competing species affect probability of successful invasion of container communities by non- native species. Specific aim 2 is to determine the importance of a trade-off between competitive and colonization success as a mechanism of species coexistence in container communities. We will test two predictions of the hypothesis that coexistence among Aedes and Ochlerotatus species results from a tradeoff between competitive and colonization abilities: Prediction 1 is that there is a competitive hierarchy among Aedes and Ochlerotatus species. This will be tested in a set of laboratory competition experiments. Prediction 2 is that species'abilities to colonize vacant sites are negatively correlated with their positions in this competitive hierarchy. We will test this prediction using a field experiment designed to quantify colonization ability of container mosquitoes. Specific aim 3 is to determine the competitive effects occurring between the two major multispecies groups of container-dwelling mosquitoes: Aedes + Ochlerotatus vs. Culex. We will develop methods for exclusion of Aedes + Ochlerotatus and use those methods to test the hypothesis that asymmetrical direct and indirect interactions between these two groups result in Aedes + Ochlerotatus presence reducing local populations of Culex. Container-dwelling mosquitoes can be a significant public health problem because many of these species are vectors of human disease (e.g., La Crosse Encephalitis, West Nile Viral Encephalitis, St. Louis Encephalitis), and because these containers often occur in close proximity to the places people live, work, and take recreation. This project investigates the effects that these mosquitoes have on one another, how those effects may influence the population dynamics of these species, and whether nonnative species can invade container communities. By investigating the structure and function of this entire community of mosquitoes, we will gain a better understanding of current and future public health threats from these vectors,